The company exploded with growth during the first quarter — expanding its entire employee base by 4,200 people, or 12 percent, in just three months, bringing its total to 37,900 employees. That’s up a massive 45 percent from 26,100 employees a year ago.

Amazon reported net sales of $9.86 billion, up 38 percent and topping analysts’ expectations of $9.54 billion. However, its profits fell 33 percent to 44 cents per share, as operating expenses exceeded $9.5 billion — up from $6.7 billion in the same quarter last year.

Here’s the official quote from Amazon CEO Jeff Bezos in the news release …

“In the last 90 days, we announced Kindle with Special Offers, Kindle Library Lending, Audible audiobooks on Kindle, Appstore for Android, Amazon for Windows Phone 7, Checkout by Amazon in both Germany and the U.K., a Kindle Store in Germany, Cloud Drive, Cloud Player, and Prime Instant Video – just to call out a few of the things we’ve been working on. We love inventing on behalf of customers and have never been more excited about the long-term opportunities.”

Update: On a conference call with analysts, Amazon executives attributed the company’s higher expenses to factors including investment in fulfillment centers, to increase capacity, as well as development of new technologies.